Alpha,alpha&#39;-bis-(2-hydroxyphenyl)-diisopropyl benzenes as stabilizers for polyurethanes

ABSTRACT

THE INVENTION RELATES TO A PROCESS FOR STABILISHING POLYURETHANES, PARTICULARLY POLYURETHANE ELASTOMER THREADS AND FILMS, AGAINST DEGRADATION AND DISCOLORATION UNDER THE ACTION OF LIGHT OR UV RADIATION, OXYGEN, ATMOSPHERIC CONSTITUENTS (E.G. NITROGEN OXIDES) AND HEAT BY THE ADDITION OF BISPHENOLS.

United States Patent P 20 12 285.4 Int. Cl. C08g 51/58, 51/60 US. Cl. 260-453 N 14 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a process for stabilising polyurethanes, particularly polyurethane elastomer threads and films, against degradation and discoloration under the action of light or UV radiation, oxygen, atmospheric constituents (e.g. nitrogen oxides) and heat by the addition of bisphenols.

The invention relates to a process for stabilising polyurethanes, particularly polyurethane elastomer threads and films, against degradation and discoloration under the action of light or UV radiation, oxygen, atmospheric constituents (e.g. nitrogen oxides) and heat by the addition of bisphenols of the general Formula I:

OH OH I CH3 CH3 I R d J R CH9 CH3 CH3 CH:

as stabilisers, in whichformula Rrepresents a straight chain or branched C to C alkyl radical, a C to C cycloalkyl radical, if desired substituted by lower alkyl radicals, or a C to C aralkyl radical,

or if desired a stabiliser mixture of the above mentioned bisphenols and UV stabilisers preferably derivatives of a 2- (2'-hydroxyphenyl) -benzotriazole.

Polyurethanes prepared from higher molecular weight polyhydroxyl compounds, polyisocyanates and chain lengthening agents, which polyurethanes are widely used in the form of foam resins, elastomers, coatings, films or elastomer threads, are unstable to light and to some extent also to air at elevated temperatures, the degree of instability depending to some extent on the components from which they have been prepared. As a result of this instability, their mechanical properties deteriorate and in many cases there occurs in addition a severe discoloration of the polyurethanes.

Many attempts have been made to protect the polyurethanes against discoloration and degradation by the addition of known antioxidants, e.g. those based on phenol, but such stabilisation is generally not sufiicient.

Thus, for example, phenols such as 4,4'-alkylidene-bis- (6-tertiary butyl)-m-eresol, 2,6-ditertiary butyl-4-methylphenol or 4,4-methylene bis (2,6-ditertiary butyl phenol) have been tested for use as stabilisers but they either impart an unwanted colour to the products right from the start or fail to protect the products against discoloration under the action of light or atmospheric constituents. Polyphenols such as 1,3,5-trimethyl-2,4,6-tris- (3,5-ditertiary butyl-4-hydroxybenzyl)-benzene have also been proposed as stabilisers (DAS No. 1,243,866). In addition, numerous phenolic compounds have been mentioned which are said to be suitable for stabilising polyurethanes 3,778,409. Patented Dec. 11, 1973 ice if used together with hydroxybenzophenones (DAS No. 1,106,490). The eifect of these phenolic stabilisers, however, is not suflicient. They are not wash-resistant and they have a colour of their own which is unacceptable, e.g. if they are used in white elastomer threads.

A new class of phenolic stabilisers has now been found which by virtue of their particular structure enables highly etfective stabilisation of polyurethanes to be achieved. These stabilisers are themselves colourless, cause no discoloration in polyurethanes and provide substantially better protection todiscoloration and degradation under the influence of visible and/or UV light and/ or atmospheric constituents (such as oxygen, nitric oxide and waste gases from combustion). In addition, the substances are readily soluble in polyurethane elastomers and do not form crystalline deposits on the surface.

The invention also relates to the use of 0.01 to 10% by weight of bisphenols of the general Formula I:

l CH: CH: a R CH: CH:

| CH: CH: (1)

in which R represents a straight chain or branched C to C alkyl radical (preferably a C alkyl radical), a C to C cycloalkyl radical which may be substituted by lower alkyl radicals, and C to C aralkyl radicals,

as stabilisers to stabilise segmented polyurethane elastomers against discoloration and deterioration of their mechanical strength.

The following are given as examples of radicals R: methyl, ethyl, n-propyl, isopropyl, n-butyl, secondary butyl, tertiary butyl, amyl, isoamyl, hexyl, isohexyl, isooctyl, isononyl; cyclopentyl, cyclohexyl, 4-methylcyclohexyl, a-methylc'yclohexyl; benzyl, a-methylbenzyl and (1,0:- dimethyl benzyl.

The bisphenols used are preferably bisphenols of the following general formula:

in which R represents a methyl, t-butyl, cyclopentyl oicyclohexyl group, 7

these bisphenols being used in quantities of 0.05 to 5.0%

byweight, based. on the polyurethane elastomers.

0.2 to 3% by weight of the. followingtstabilisers, based on the polyurethane elastomers, are advantageously used:

(III) O OH CH! H The a,a'-bis-(Z-hydroxyphenyl) 1,4 diisopropyl benzenes used according to the invention, which will hereinafter be referred to briefly as bisphenols, are new compounds and can be prepared by the reaction of a,a'-dihydroxy-l,4-diisopropyl benzene with ortho-substituted 4- methylphenols in the presence of acid dehydration catalysts, water being split 01f in the process; e.g. according to the following reaction equation:

in which formula, R has the meaning already given for Formula I.

The substantial improvement which can be obtained by using the new bisphenols is demonstrated by comparison tests in which they are compared with a commercial mononuclear phenol 2,6-ditertiary-butyl-p-cresol, a binuclear phenol methylene-bis-(2-hydroxy-3-tertiary butyl- 5-methyl phenol) and a trinuclear phenol 1,3,5-trirnethyl-2,4,6-tris-(3,5 ditertiary butyl-4-hydroxlbenzyl) benzene -(X). Two other examples, in which a bisphenol unsubstituted in the ortho-position (VI) and a bisphenol having OH groups in the p-position (VII) (as described in Belgian patent specification No. 604,516) were used, demonstrate the strict dependence between the action and the constitution of the bisphenols.

on on (in; rim I I Q CH:

CH: CH: (VI) on, on,

CH: CH: no 5 -4 011 CH; CHI cm cm W) These experiments show, among other things, that the phenols conventionally used as stabilisers, which are similar in structure to the phenols represented in the above formulae but which instead of the C(CH group have only a CH group between the benzene rings, e.g. bisphenols or trisphenols such as:

on on CIQ I /CH3 CH3; 0 CH: C (CH: CH3 CH3 on, om (vrn on on on onmogongcmgownm CH3 CH; CH: (IX) dilfer from the stabilisers according to the invention in that they themselves undergo strong discoloration (yellowing) when exposed to UV light and are therefore unsuitable for stabilising colourless polyurethanes. In addition, the bisphenols according to the invention show better stabilisation against degradation than, for example, the known phenolic stabiliser 1,3,5-trimethyl-2,4,6-tris-(4-hydroxy-3,5-ditertiary butyl benzyl) benzene (according to DAS No. 1,243,866). A relatively slight modification of the structure of the phenols according to the invention, e.g. a shift of the alkyl radicals, results in a substantial reduction in the stabilisation effects and, in some cases, yellow discoloration is observed (see comparison tests).

The efiicient stabilising effect of the special phenolic compounds according to the invention, which is so significant for polyurethane elastomers, was unexpected and could not have been predicted.

Surprisingly, the elfect of the phenols is not entirely dependent upon the presence of a tertiary alkyl radical in the ortho-position to the hydroxy group, and compounds which have a secondary or primary alkyl radical are equally efficient.

The invention also relates to the use of 0.05 to 5.0% by weight of a stabiliser mixture consisting of:

(a) bisphenols according to the invention and, in addition (b) 2-(2'-hydroxyphenyl) benzotriazoles for stabilising polyurethanes.

Bisphenols of the following Formula I are used:

OH OH CH; CH: l R +Q+ R om CH:

CH; CH;

in which R has the meaning already given.

2 (2'-hydroxyphenyl)-benzotriazolcs of the following formula are used:

-' benzotriazole 2 (2hydroxy- 3 ,5 diter'tiary octylphenyl) -benzotriin which X-represents a hydrogen atom,-an alkyl group or a halogen atom,

.Y represents a hydrogen atom, a C to C alkyl radical or an alkylene radical having hereto atoms, preferably a tertiary alkyl radical such as tertiary butyl, tertiary amyl or tertiary dodecyl, and I vR represents hydrogen or a C to C alkyl radical, e.g.

. methyl, ethyl, isopropyl, tertiary butyl, tertiary amyl,

tertiary octyl or .tertiary dodecyl.

-The mixture is-used in proportionsby weight of compound A to compound B of 1:10 to 10:1, the polyurethan'e elastorners therebyundergoing a synergistic stabilisation against discoloration and degradation under the action of light, heat and atmospheric constituents.

The use of 2 (2-hydroxyphenyl)-benzotriazoles as stabilising additives to polymers is known per se but is entirely inadequate :when used .as the only means of stabilisation. A combination of 2-(2'-hydroxyphenyl)-benzotriazoles' and 1,3,5 trimethyl 2,4,6-tris-(3,5-ditertiary butyl-4-hydroxybenzyl)benzene or 1,2,4,5-tetramethyl-3,6- bis-(3,5 ditertiary butyl-4-hydroxybenzyl) benzene has also been'described in Dutch Auslegeschn'ft NE 6509745 for stabilising segmented polyurethanes. These additives do provide a certain amount of protection but it is insufiicient and the need for a highlyefiicient, resistant stabilisation of elastomers, particularly of elastomer threads,

rema1ns.

In the preferred embodiment of the invention, the compound (b) used is one ofthe benzotriazoles of the following formula:

l in which I X represents a hydrogen or chlorine atom,

Y represents a hydrogen atom' or a C to C alkyl radical, preferably a tertiary alkyl radical, such as tertiary butyl or tertiary amyl or an N-methylenephthalimido radical, and

R represents-a hydrogen 'atom, a Ci to C alkyl radical, e.g. methyl ethyl,'isopropyh'tertiary butyl or tertiary amyl radical. v.

The followingcompounds are given as examples of light protective'agents based on'"2 (2-hydroxyphenyl)- 1- (2'-hydroxy-5 'rmethylphenyl -ben zotriazole,

1- 2'-hy droxy-5 '-methylphenyl) -5-chloro-benzotriazole,

.; 2-(2-hydroxy-3'tertiary butyl-j-methylphenyl)-benzotriazole, 2-(2-hydroxy-3-tertiary butyl-S-methylphenyl)-5-chlorobenzotriazole, j i '2- (2-hydroxy 3 '-methyl-5-tertia'ry" butylphenyl) -benzotriazole, 1

butylphenyl) -5- chloro-beniotriazole,

2- (2'-hydroxy- 3 ,5 -dimethylpheny1eniotriazole,

; '21- 2'- hydroxy 3f,5f-dimethylphenyl)-5-ehloro-benzov triazole,

2- (2fehydroxy-3f,5f-ditertiary amylphenyl)-benzotriazole, 4 I: :2:(2' hydroxy-3',5'-ditertiary zimylphenyD-S-chloro- .beniotriazole; I

azol e,

6 2-(2-hydroxy-3',5-ditertiary octylphenyl)-5-chlorobenzotriazole, and 2- (2'-hydroxy-3 '-N-methylene-phthalimido )-benzotriazole.

Other suitable hydroxyphenyl benzotriazoles are mentioned, for example, in German Auslegeschrift No. 1,213,408; 1,213,409 and 1,213,410 and in US. patent specification No. 3,213,508. Known polyurethane stabilisers (see, for example, German Auslegeschrift No. 1,157,386) may also be added.

The elastic polyurethane which are to be stabilised, which may be in the form of foams, can be obtained by known processes and from known starting materials. The polyurethanes are generally prepared by reacting higher molecular weight polyhydroxyl compounds (e.g. polyesters or polyethers having a molecular weight of about 500 to 5000, melting points preferably below 60 C.) with aliphatic, araliphatic or aromatic polyisocyanates (preferably aromatic diisocyanates such as toluylene diisocyanate or dihpenylmethane-4,4'-diisocyanate) and socalled chain lengthening agents, i.e. low molecular weight compounds (molecular weight e.g. 18 to 400) which have two or more groups that are reactive with isocyanate (e.g. water, low molecular weight diols, diamines, dihydrazides or similar compounds, e.g. aminoalcohols, aminohydrazides, hydroxy hydrazides, aminosemicarbazides, semicarbazido hydrazides, semicarbazido carbazic esters or mixtures of these chain lengthening agents) in a single stage or in a multi-stage process in me melt or in solvents. Numerous known processes or modifications thereof may be employed for this reaction.

The following are given as examples of starting materials: polyesters of adipic acid and dialcohols containing 2 to about 10 carbon atoms, preferably those containing more than 5 carbon atoms, the dialcohols, if desired, being also used for lowering the melting points of the polyesters in the mixture; polyesters of caprolactone and dialcohols, polyalkylene ether diols, especially polytetramethylene ether diols, polytrimethylene ether diols, polypropylene glycol or the corresponding copolyethers. The diisocyanates used are preferably aromatic diisocyanates, such as diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, araliphatic diisocyanates such as m-xylylene diisocyanate or aliphatic diisocyanates such as hexamethylene diisocyanate and dicyclohexylmethane-4,4-diisocyanate. These starting materials are reacted together, if desired, with the addition of other dialcohols, to form NCO prepolymers which preferably have the structure indicated in Belgian patent specification No. 734,194. Suitable chain lengthening agents, which may be used as mixtures or in a stepwise reaction, include water and/or dialcohols or trialcohols such as butane diol and p-xylylene glycols, trimethylol propane, aminoalcohols such as ethanolamine, diamines such as diphenylmethane-4,4'-diamine, 3,3-dichloro-diphenylmethane-4,4'-diamine, but preferably aliphatic diamines such as ethylene diamine, 1,2-propylene diamine, isophorone diamine, metaxylylene diamine and hydrazine or dihydrazides such as carbodihydrazide, oxalic acid dihydrazide, glutaric acid dihydrazide, pimelic acid dihydrazide, terephthalic acid dihydrazide or semicarba- 'zidohydrazides such as fi-semicarbazide alanyl hydrazide; if desired, they may be used as mixtures ofchain lengthen ing agents.

The polyurethanes'tobe stabilised are preferably of j the type which, in addition to urethane groups, also contain NHCONH groups obtained by reacting isocyanate groups with water a'nd/orwith compounds containing NH end groups (e.g. diamines, dihydrazides, carbodihydrazide, semicarbazido hydrazides, orhydrazine) and which have a substantially linear, segmented molecular structure, are, soluble in highly polar solvents such as climethylformamide or dimethyl acetamide before they 7 are shaped and whose characteristic segments may be represented by the following formula:

which may be obtained by reacting an NCO prepolymer OCN.Y.NCO with a chain lengthening agent N N.X.NH

The radical Y of the NCO prepolymer may, for example, have the following structure:

or another of the usual structures (see Belgian patent specification No. 734,194).

In the above formula R represents a divalent aliphatic, araliphatic or aromatic radical (of a diisocyanate),

D represents the radical of a higher molecular weight polyhydroxyl compound having a molecular weight of 500 to 5000 and melting points below 60 C. without its terminal hydroxyl groups (eg the radical of a polyalkylene ether, polyester, polyacetal or poly-N-alkyl urethane),

X represents the radical of a divalent chain lengthening agent which has terminal NH groups but without the terminal NH; groups, e.g. an aliphatic, araliphatic, aromatic or heterocyclic radical, an HN-CO-alkylene- CONH radical, an

radical, a bond between two N atoms.

The synthesis of such polyurethane (ureas) has been fully described, e.g. in German Auslegeschrift No. 1,270,276 and in Belgian patent specification No. 734,194. Polyurethane foam resins can be prepared by known processes and formulations, e.g. with the addition of stabilisers to the starting components (e.g. polyethers) (see eg Kunststolf-Handbuch, vol. VII, Polyurethane, publishers Carl Hanser Verlag, Munich, 1966, pp. 440-457, 50453l).

The stabilizers may be incorporated in the polyurethanes by any method adapted to the technical process requirements. The simplest method consists of adding the stabilizers, if desired in the form of solutions, to solutions of the polyurethanes, e.g. their solutions in highly polar solvents such as dimethyl formamide or dimethyl sulphoxide which is the form in which they are preferably used for spinning, coating or coagulation purposes. Alternatively, the stabilizers may be incorporated in the melts or plasticised polyurethane sheets by means of suitable mixing devices such as kneaders or rollers. In the case of elastomer threads, the stabilisers may also be applied to the surface together with the dressing.

Another possibility lies in adding the stabilisers to the starting materials used for the preparation of the polyurethanes and only then carrying out the polyurethane synthesis. Thus, for example, bisphenol compounds are soluble in higher molecular weight polyhydroxyl compounds (e.g. polyesters or polyethers). The polyurethane synthesis, e.g. production of foam resins or elastomers, can then be carried out with such polyesters or polyethers which already contain stabiliser. The stabilizers may also be added to the diisocyanates or to the prepolymers of higher molecular weight polyhydroxyl compounds and (excess molar quantities) of diisocyanates before the formation of polyurethane is carried out, e.g. by spinning it into aqueous diamine solutions. Discoloration of the polyurethanes can be prevented during synthesis of the polyurethanes by using the stabilisers in the reaction of NCO prepolymers with chain lengthening agents such as diamines, hydrazine, hydrazides or similar chain lengthening agents in highly polar solvents such as dimethyl formamide or dimethyl acetamide. The quantity of stabilisers added is 0.01 to 10% by weight, preferably 0.2 to 3.0% by weight.

The light-protective action is enhanced by adding the stabilisers according to the invention to polyurethanes which contain 0.02 to 1 mol, preferably 0.05 to 0.3 mol, per kg. of elastomer substance, of reactants which contain aliphatically substituted tertiary amino groups. Examples of such reactants are glycols, diamines, dihydrazides or polyesters or polyethers containing tertiary amino groups, e.g. N,N-bis-(B-hydroxypropyl)-methylamine, N,N-bis-(fl-hydroxyethyl)-piperazine, N,N'-dimethyl ethylene diamine, N,N-bis-('y-aminopropyD-ethylene diamine, N,N-bis-('y-aminopropyD-piperazine or polyethers which contain tertiary amino groups, or polyesters which contain tertiary amino groups, which compounds are prepared from dialcohols which contain tertiary amino groups.

Preparation of the bisphenols of the general Formula I according to the invention Synthesis of the bisphenols may be carried out by reacting u,a-dihydroxy-1,4-diisopropyl benzene with orthosubstituted 4-methylphenols (water being split off) in the presence of acid dehydration catalysts such as p-toluene sulphonic acid, phosphoric acid, sulphuric acid, hydrochloric acid or strongly acid ion exchangers.

The water formed on condensation may, if desired, be removed by azeotropic distillation. Suitable solvents e.g., are benzene, cyclohexane, cleaning petrol, toluene, xylene and chlorinated hydrocarbons such as chloroform, carbon tetrachloride and tetrachloroethylene.

Another process for the preparation of the bisphenols according to the invention consists in condensing a,a'- dihydroxy-1,4-diisopropyl benzene with 2 molecules of p-cresol with elimination of water by the process mentioned above and then alkylating, cyclolalkylating or aralkylating the free ortho-positions with suitable olefines or carbinols.

Processes of this type are known as such and do not constitute a subject of the present invention.

The following examples serve rather to explain more fully the preparation of the bisphenols according to the invention and of compounds VI and VII used for comparison tests.

od-Bis-(Z-hydroxy-3,5-dimethylphenyl)-1,4-diisopropyl benzene (Compound H above) 220 g. (1.8 mol) of 2,4-dimethylphenol, 97 g. (0.5 mol) of a,ot'-dihydroxy-1,4-diisopropyl benzene and 500 ml. of xylene were boiled for one hour in a water separator with the addition of 5 g. of p-toluene sulphonic acid, 18 ml. of water being separated. After cooling, 500 ml. of petroleum ether were added to the mixture, the mixture was cooled to 5 C., and the colourless crystals which separated were removed by suction filtration. They have a melting point of 178 C. to 179 C.

C H O (molecular weight: 402).Calculated (percent): C, 83.58; H, 8.46; O, 7.96. Found (percent): C, 83.9; H, 8.7; 0, 7.9.

a,u-Bis-(2-hydroxy-3-tertiary butyI-S-methyIphenyD-IA diisopropyl benzene (Compound HI above) 164 g. (1 mol) of Z-tertiary butyl-p-cresol, 49 g. (0.25 mol) of a,a'-dihydroxy-1,4-diisopropyl benzene and 2.5 g. of p-toluene'sulphonic acid in 400 ml. of cleaning petrol were boiled in a water separator for one hour, 9 ml. of water being separated. 2 g. of ammonia were introduced to neutralise the catalyst. The mixture was filtered and completely distilled under 'vacuum at temperatures of up to 100 C. On the addition of methanol, a colourless powder precipitated. This was filtered 01f under suction and dried. M.P. C.

ing'pet water-being separated. 1 g. of ammonia was in- 9 C H O (molecular weight: 486).Calculated (percent): C, 83.95; H, 9.47; O, 6.58. Found (percent): C,

352 g. (2'mol) of-Z-cycIopentyI-p-cresol, 97 g. (0.5 mol) of..a,bz.'.-dihydroxy-1,4:diisopropyl benzene and 5 g. of p-toluene sulphonic acid in 500 ml. of cleaning petrol wereboiled'in a water. separator for 2 hours, 18 ml. of water being separated. 2 g. of ammonia were introduced, the solution was J filtered', and 50 ml. of methanol were added. The precipitated crystals were purified by recrystallisation from; toluene. Colourless crystals, M.P. 220 C. .,.C H O (molecular weight: 510).i- Calculated (percent): C, 847; H, 9.02;"0, 6.28. Found (percent): C, 83.9; H, 9.1 O, 6.3.:-

" odd-Bis-(2-hydroxy 3-cyclohexyl-S-rnethylphenyl)-1,4-

- diisopropyl-benzene (Compound V above) o d-Bis-(2-hydroxy-5-methylphenyl)-1,4-diisopropyl benzene (Compound VI above) 216 g. (2 mol) of p-cresol, 97 g. (0.5 mol) of a,a'-di- .hydroxy;1,4;diisopropy1 benzene, .5 g. of p-toluene sulphonic acid and 500 m1; of cleaning'petrol were boiled in a water separator for 'l hour, 18 m1. of water being 7 separated,j'1"he' crystallised product was removed by suc-.

tion'filtra at 0 'C. and-recrystallised from benzene. "Colourless "crystals, P. 183 'C.

"' C Hg O (molecular weight: 374).Calculated (percent): C, 83.42; H, '8.02;O, 8.56. Found (percent):

troduced into the hot solution. After filtration and when the solution was cold, 250 ml. of petroleum ether were added and the crystalpaste which precipitatedwas removed by suction filtration at 0 C. and recrystallised from toluene. Colourless crystals, M.P. 160 C.

(3 1-1 0 (molecular weight: 402).-Calculated (percent): C, 83.58; H, 8.46; O, 7.46. Found (percent): C, 83.6; H, 8.6; O, 8.2.

The following examples are to further illustrate the invention without limiting it.

EXAMPLE 1 500 parts of a polytetramethylene ether diol (molecular weight 1010), 104 parts of N,N-bis-(/8-hydroxy propyl)-N-methylamine, 1822 parts of diphenylmethane- 4,4'-diisocyanate and 1740 parts of chlorobenzene were heated to C. to 68 C. for 68 minutes and then cooled to room temperature. 6450 parts of this NCO prepolymer solution (2.05% NCO based on solid substance) are introduced in the course of 1O minutes with vigorous stirring into a fresh suspension prepared by the addition of parts of solid carbon dioxide to a solution of 73.7 parts of ethylene diamine and 4.68 parts of 1,2-propylene diamine in 13,440 parts of dimethyl formamide, a homogeneous, slightly yellowish elastomer solution being obtained which is pigmented by the addition of 4% by weight (based on elastomer solid substance) of titanium dioxide (rutile). The elastomer solution (viscosity 610 poises) is made up into films in separate portions with and without the addition of stabiliser in the usual manner and the films are cut up into threads which are then exposed to UV light (fadeometer) (see Table 2). Portions of these elastomer solutions are spun by the usual dry spinning process and the threads are exposed to light in a xenon test with and without the addition of stabiliser (see Table 1). If the 2% by weight of stabiliser are not added subsequentlyto the finished elastomer solution but dissolved in dimethyl formamide together with the diamines and the elastomer solution is then prepared from the NCO prepolymer, a colourless elastomer solution is obtained which does not undergo discoloration when exposed to air. After formation of the films and exposure of the threads to light, the stabilising effect against degradation of mechanical strength under exposure to light was found to be practically identical.

TAB LE 1 Lossiustrength ot elastomer threads produced by the dry spinning process (individual denier approx. 10 dtex., total denier approx. 220 dtex.) after Xeno test exposure 122 g. '(1"m'ol)of -2-'hydrox'y-1,3-dimethyl benzene,-49 g. (0.25 mol) of ,a'-dihydroxy-1,4-diisopropyl benzene, 2.5 g. of ,pitcdu'eriev sulphonic acidand 300 ml. of clean- 5 i l were "boiled in awate'r' separator for one hour,

Before exposure 72 hours hours j Elonga- Elonga- Elongag Ultimatetensile tion at Ultimate tensile tion at Ultimate tensile tion at strength, break, strength, break, strength, break,

g./dtex. percent g./dtex. percent gJdtex. percent Remarks Without stabiliser---" 0.59, colourless. 506 0.17, ye1lowish 372 No longer measurableyellowish-yellow 1% stabiliser II 0.61, colour1ess-- 500 Colourless 0.40, colour1ess 480 Yellowish only after more than 200 hours. 2% stabiliser II 0.66, co1onr1ess-- 510 .....do 0.52, c0lour1ess 525 Yellowish only after about 225 hours. 1.33% stabiliser plus .de 510 0.63, eo1our1ess.- 510 0.60, colourless 512 synergistically active mixture. Yellowish 0.67% 2-(2-hyonly after about 300 hours. droxy3-t-butyl-5- methylphenyl) beur zotriazole.

,. w, t;B1s.-..(4-hydroxy-3,i dimethylphenyl) l,4-d11sopropyl 1 Example 2 The bisphenols and comparison stabilisers shown in the table are dissolved in the elastomer solution (according to Example 1) in the quantities indicated. After casting of the elastomer solution and drying to produce films, the films are cut up into strips which are then exposed in -the fadeometer for the length of time indicated.

TAB LE 2 Fadeometer exposure of film strips or out threads After fadeometer exposure of Before exposure 22 hours 44 hours 66 hours Elonga- Elonga- Elonga- Elonga- Ultimate tensile tion, Ultimate tensile tion, Ultimate tensile tion, Ultimate tensile tion, strength, gJdtex. percent strength, g./dtex. percent strength, g./dtex. percent strength, g.ldtex percent Stabilisers added- I Without stabiliser 0.56, colour1ess...- 657 0.04, yellow No longer measurable-Enable films, severe cracking, I elongation Plus 2% stabiliser II 0.72, colourless. 651 0.70, eolourless 652 0.62, almost colour- 662 0.58, almost 653 less. colourless: 2% UV absorber Colourless 0.39, yellowish- 525 No longer measurable, yellow. 1% hstablilisler Ilium, tri- 0.55, colourless. 613 0.50, colourless- 620 0.46, colourless. 637 0.41, colourless. 616

eny p 05 e. i 1 o stabiliser I I, 1% tri- 0.46, colourless- 590 0.43, ahnost 630 0.40, yellowish. 697 0.39, yellowish. 678

phenyl phosphine. colourless.

Plus 1.33% stabiliser II, Colourless Colourless 1 Colourless 2 Almost colourless I 0.66% UV absorber. less. 2% stabilise! III- do). do. Almost colourless Pale yellowish 1 pale yellowish. 2% stabiliser IV dofldo. do. do... 2% stabiliser V dofi. do!" dofl- Almost colourless, pale yellowlowlsh.

Comparison tests: 2% Compound VI .-do Yellow (already Intense yellow 5 Intense yellow from hours onwards) J 2% Compound VII- do. do.*.... do. do. 2% 1,3, 5-trlmcthyl 2, 4,6- do Almost colourless, Yellow Severe degradahis-(3, sditertiary yellowish. tion, intense butyli-hydroxyyellow. benzyl)-benzene (Compound X).

Strength relatively well preserved v 2% Compound IX Almost colourless Strong yellow Intense yellow Yellow brown.

l 2-(2'-hydroxy-3-tertiary butyl-5-methylphenyl)-5-chlorobenzotriazole.

2 Strength substantially preserved, no crack formation on elongation.

Films show severe crack formation on elongation with increasing time and substantially reduced ultimate tensile strength.

As shown by the results, a very good improvement is achieved with the stabilisers according to the invention, both as regards preservation of the mechanical strength and as regards reducing the discoloration, and this improvement can be further enhanced by the addition of UV absorbers of the Z-hydroxyphenyl-benzotriazole type. The addition of triphenyl phosphite or triphenyl phosphine does not provide any substantial improvement. Compounds VI and VII, which differ only slightly in their structure from the stabilisers according to the invention, are substantially inferior since they undergo severe discoloration and their protective action is much weaker. Known stabilisers such as compound IX or X are also distinctly inferior in their stabilising eifect, the polyurethane either continuing to undergo severe degradation or preserving its strength relatively well but undergoing severe discoloration.

Example 3 '600 parts of a copolyester of adipic acid, hexane-1,6-diol and 2,2 dimeth'ylpropane-L3-diol containing diol in the molar proportion of 2:1 (OH number 65.6) are heated to 45 C. to 51 C. for min'utes'with 11.6 parts of N,N'-bis-(B-hydroxypropyl)-methylamine, 160.3 parts of diphenylmethane 4,4-diisocyanate and 192 parts of dimethyl formamide and 0.1 partof a 35% solution of SO, in dioxane until the NCO content has dropped to2.08% (based on solid NCO prepolymer). v

532 parts of this prepolymer solution are'stirred into a solution of 17.15 parts of fl-semicarbazido propionic acid hydrazide in 34 parts of water and 1119 parts of dimethyl formamide, and 0.2 part of hexane-1,6-diisocyanatc and 4% by weight of titanium dioxide are added to the clastomer solution. a v V Stabilisers are dissolved in this elastomer solution in the percentages by weight shown in Table 3' (based on solid substance of elastomer), cast to form films in the usual manner which are cut up into threads and exposed to the fadeometer.

TABLE 3 Fadeometer exposure on film strips After fadeometer exposure of- Before exposure 22 hours 44 hours 66 hours Ultimate tensile Elonga- Ultimate tensile Elonga- Ultimate tensile Elonga- Ultimate tensile Elongastrength, tion, strength, tion, strength, tion, strength, tion, g./dtex. percent g./dtex. percent gJdtex. percent g./dtex. percent Additions of stabiliser- I Without stabilizer-.. 0.60, colourless. 666 0. 50, pale yellowish. 620 0.27, yellow brown 538 No longer mgasurableye ow rown Plus 2% stabiliser II. 0.66, colourless- 687 0.66, colourless 763 0.62, colourless 681 0.60, colourless. 680

Strength preserved, surface Smooth and homogeneous when stretched 2% stabiliser IV... Colourless Colourless- Almost colourless- Comparison examples: i f,

Compound IX, 2%. Almost colourless. Lemon yellow Intense lemon yellow Yellow brown. 2% Compound X.-. Colourless Pale yellowish Pale yellowish brown Yellowish brown. 2% Compound VIII do- Yellowish to yellow Yellow. Yellow I 1 Surface of the films breaks up into a large number of cracks when stretched owing to orosslinking on the surface a v 'ExampleA The segmented polyurethane elastomer of claim 1, 1 600 parts of-the eopolyest'ei desdribed in Example 3 sad stabmzer having the formula are heated to-85 Gsin'th'efmelt for 3 8 minutes with 173.4 partsj'of diphenylmethanel-fi diisocyanate and 11.9 parts of N,N' bis-(fi hydroxypropyl) rnethylamine, and the rer 5 H OH sulting N60=prepolymer =melt (2.76% NCO) 1s lntro- Ha CH: duced into a solution heatedto 80? C. of 23.0 parts of H H carbodihydrazide'in2431 parts of dimethyl formamide i 6 with the addition of 32,-;parts of T10 a highly viscous (5301*) elastomer solution being formed. 10

The stabilisers or comparison jsubstances shown in Table 4 are added to this elastomer solution which is then exposed to light in thefadeometer in the form of film strips.

TABLE 4 Fudeometer exposure of film strips (approx. 350 dtex.)

After fadeometer exposure of- Before exposure 22 hours 44 hours 66 hours Ultimate tensile Elonga- Elonga- Elonga- Elongastrength, on, Ultimate tensile tion, Ultimate tensile tion, Ultimate tensile strength, tion, g./dtex. percent strength, g./dtex. percent strength, g.ldtex. percent g./dtex. percent Additions of stabiliser- Without stabiliser 0.62 550 0.43, yellowish 502 0.22, yellowish... 385 No longer measurable Pius2%stabiliser1I 0.63 581 0.67, eolourless....- 595 0.60, colourless...-. 567 0.47,almostcolourless 495 What we claim is: 8. The segmented polyurethane elastomer of claim 1, 1. A segmented polyurethane elastomer having insaid stabilizer having the formula cluded therein 0.01 to 10 percent by weight of a stabilizer OH OH of the general formula EH8 in; 0H cm 011 $11. dug

OH; R R

cm CH:

9. A segmented polyurethane elastomer having included therein 0.01 to 10 percent by weight of a stabilizer mixture of a a bis henol of the eneral formula in which R is either a straight or branched chain alkyl P H g group containing 1 to 18 carbon atoms, a cycloalkyl group 0 containing 5 to 6 carbon atoms which may be substituted R I QQ R by one or more lower alkyl groups, or an aralkyl group a 6 containing 7 to 9 carbon atoms. H3 H8 2. The segmented polyurethane elastomer of claim 1, wherein the R in said formula represents methyl, t-butyl, cyclopentyl or cyclohexyl.

3. The segmented polyurethane elastomer of claim 1, having included therein 0.05 to 5 percent by weight of Ha Ha in which R is either a straight or branched chain alkyl group containing 1 to 18 carbon atoms, a cycloalkyl group containing 5 to 6 carbon atoms which may be said stabilizer substituted by one or more lower alk 1 groups, or 4. The segmented polyurethane elastomer of claim an aralkyl group containing 7 to 9 capbgn atoms, and having mcluded therem 0.2 to 3 percent by weight of said (b) a benzotriazole of the formula stabilizer.

5. The segmented polyurethane elastomer of claim 1, R1 said stabilizer having the formula 0 Q X 0H 0H on. em N H Y CH 0H, wherein X is a hydrogen or halogen atom or an alkyl H 6 group, Y reprments hydrogen, a C to C alkyl radical or an N-methylene-phthalimido radical, R is a hydrogen atom or an alkyl group containing 1 CH; OH; to 12 carbon atoms,

the ratio by weight of said compound (a) to said com- 6. The segmented polyurethane elastomer of claim 1, Pound being fIOm 1011 to 1110- said stabilizer having h f l 10. The segmented polyurethane elastomer of claim 9, having included therein 0.5 to 5 percent by weight of OH OH said stabilizer mixture. CH: OH; CH: CH; 11. Threads consisting essentially of a segmented polyi 4 urethane elastomer of claim 1.

g (12H. 5 12. Threads consisting essentially of a segmented poly urethane elastomer of claim 9.

13. Films consisting essentially of a segmented polyurethane elastomer of claim 1.

14. Films consisting essentially of a segmented polyurethane elastomer of claim 9.

References Cited UNITED STATES PATENTS Hinkamp 25249.8 Nast et a1. 2602.5 Dietzler 26045.95 Hunt 260859 Megna et a1 260-45.8 Schnell et a1. 26047 Spacht 260---45.95 Swart et a1. 26045.7 

